Plasma uniformity control by gas diffuser hole design

ABSTRACT

Embodiments of a gas diffuser plate for distributing gas in a processing chamber are provided. The gas distribution plate includes a diffuser plate having an upstream side and a downstream side, and a plurality of gas passages passing between the upstream and downstream sides of the diffuser plate. The gas passages include hollow cathode cavities at the downstream side to enhance plasma ionization. The depths, the diameters, the surface area and density of hollow cathode cavities of the gas passages that extend to the downstream end can be gradually increased from the center to the edge of the diffuser plate to improve the film thickness and property uniformity across the substrate. The increasing diameters, depths and surface areas from the center to the edge of the diffuser plate can be created by bending the diffuser plate toward downstream side, followed by machining out the convex downstream side. Bending the diffuser plate can be accomplished by a thermal process or a vacuum process. The increasing diameters, depths and surface areas from the center to the edge of the diffuser plate can also be created computer numerically controlled machining. Diffuser plates with gradually increasing diameters, depths and surface areas of the hollow cathode cavities from the center to the edge of the diffuser plate have been shown to produce improved uniformities of film thickness and film properties.

CROSS-REFERENCE TO OTHER APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/207,227 (APPM/9162C02), filed Aug. 10, 2011, which is a continuationof U.S. patent application Ser. No. 10/889,683 (APPM/9162), filed Jul.12, 2004, which issued as U.S. Pat. No. 8,083,853 on Dec. 27, 2011,which claims benefit of U.S. Provisional Patent Application Ser. No.60/570,876 (APPM/9162L), filed May 12, 2004. Each of the aforementionedpatent applications is herein incorporated by reference.

BACKGROUND OF THE DISCLOSURE

1. Field of the Invention

Embodiments of the invention generally relate to a gas distributionplate assembly and method for distributing gas in a processing chamber.

2. Description of the Background Art

Liquid crystal displays or flat panels are commonly used for activematrix displays such as computer and television monitors. Plasmaenhanced chemical vapor deposition (PECVD) is generally employed todeposit thin films on a substrate such as a transparent substrate forflat panel display or semiconductor wafer. PECVD is generallyaccomplished by introducing a precursor gas or gas mixture into a vacuumchamber that contains a substrate. The precursor gas or gas mixture istypically directed downwardly through a distribution plate situated nearthe top of the chamber. The precursor gas or gas mixture in the chamberis energized (e.g., excited) into a plasma by applying radio frequency(RF) power to the chamber from one or more RF sources coupled to thechamber. The excited gas or gas mixture reacts to form a layer ofmaterial on a surface of the substrate that is positioned on atemperature controlled substrate support. Volatile by-products producedduring the reaction are pumped from the chamber through an exhaustsystem.

Flat panels processed by PECVD techniques are typically large, oftenexceeding 370 mm×470 mm. Large area substrates approaching and exceeding4 square meters are envisioned in the near future. Gas distributionplates (or gas diffuser plates) utilized to provide uniform process gasflow over flat panels are relatively large in size, particularly ascompared to gas distribution plates utilized for 200 mm and 300 mmsemiconductor wafer processing.

As the size of substrates continues to grow in the TFT-LCD industry,film thickness and film property uniformity control for large areaplasma-enhanced chemical vapor deposition (PECVD) becomes an issue. TFTis one type of flat panel display. The difference of deposition rateand/or film property, such as film stress, between the center and theedge of the substrate becomes significant.

Therefore, there is a need for an improved gas distribution plateassembly that improves the uniformities of film deposition thickness andfilm properties.

SUMMARY OF THE INVENTION

Embodiments of a gas distribution plate for distributing gas in aprocessing chamber are provided. In one embodiment, a gas distributionplate assembly for a plasma processing chamber comprises a diffuserplate having an upstream side and a downstream side, and inner and outergas passages passing between the upstream and downstream sides of thediffuser plate and comprising hollow cathode cavities at the downstreamside, wherein the hollow cathode cavity volume density of the inner gaspassages are less than the hollow cathode cavity volume density of theouter gas passages.

In another embodiment, a gas distribution plate assembly for a plasmaprocessing chamber comprises a diffuser plate having an upstream sideand a downstream side, and inner and outer gas passages passing betweenthe upstream and downstream sides of the diffuser plate and comprisinghollow cathode cavities at the downstream side, wherein the hollowcathode cavity surface area density of the inner gas passages are lessthan the hollow cathode cavity surface area density of the outer gaspassages.

In another embodiment, a gas distribution plate assembly for a plasmaprocessing chamber comprises a diffuser plate having an upstream sideand a down stream side, and a plurality of gas passages passing betweenthe upstream and downstream sides of the diffuser plate, wherein thedensities of hollow cathode cavities gradually increase from the centerto the edge of the diffuser plate.

In another embodiment, a plasma processing chamber comprises a diffuserplate having an upstream side and a downstream side, inner and outer gaspassages passing between the upstream and downstream sides of thediffuser plate and comprising hollow cathode cavities at the downstreamside, wherein the hollow cathode cavity volume density of the inner gaspassages are less than the hollow cathode cavity volume density of theouter gas passages, and a substrate support adjacent the downstream sideof the diffuser plate.

In another embodiment, a plasma processing chamber comprises a diffuserplate having an upstream side and a downstream side, inner and outer gaspassages passing between the upstream and downstream sides of thediffuser plate and comprising hollow cathode cavities at the downstreamside, wherein the hollow cathode cavity surface area density of theinner gas passages are less than the hollow cathode cavity surface areadensity of the outer gas passages, and a substrate support adjacent thedownstream side of the diffuser plate.

In another embodiment, a plasma processing chamber comprises a diffuserplate having an upstream side and a down stream side, a plurality of gaspassages passing between the upstream and downstream sides of thediffuser plate, wherein the densities of hollow cathode cavitiesgradually increase from the center to the edge of the diffuser plate,and a substrate support adjacent the downstream side of the diffuserplate.

In another embodiment, a gas distribution plate assembly for a plasmaprocessing chamber comprises a diffuser plate having an upstream sideand a down stream side and the gas diffuser plate are divided into anumber of concentric zones, and a plurality of gas passages passingbetween the upstream and downstream sides of the diffuser plate, whereinthe gas passages in each zones are identical and the density, thevolume, or surface area of hollow cathode cavities of gas passages ineach zone gradually increase from the center to the edge of the diffuserplate.

In another embodiment, a method of making a gas diffuser plate for aplasma processing chamber, comprises making a gas diffuser plate to havean upstream side and a down stream side, and a plurality of gas passagespassing between the upstream and downstream sides of the diffuser plate,bending the diffuser plate to make it convex smoothly toward downstreamside, and machining out the convex surface to flatten the downstreamside surface.

In another embodiment, a method of making a gas diffuser plate for aplasma processing chamber comprises machining a gas diffuser plate tohave an upstream side and a down stream side, and a plurality of gaspassages passing between the upstream and downstream sides of thediffuser plate, wherein densities, volumes or surface area of hollowcathode cavities of the diffuser plate gradually increase from thecenter to the edge of the diffuser plate.

In another embodiment, a method of depositing a thin film on a substratecomprises placing a substrate in a process chamber with a gas diffuserplate having an upstream side and inner and outer gas passages passingbetween the upstream and downstream sides of the diffuser plate andcomprising hollow cathode cavities at the downstream side, whereineither the hollow cathode cavity volume density, or the hollow cathodecavity surface area density, or the hollow cathode cavity density of theinner gas passages are less than the same parameter of the outer gaspassages, flowing process gas(es) through a diffuser plate toward asubstrate supported on a substrate support, creating a plasma betweenthe diffuser plate and the substrate support, and depositing a thin filmon the substrate in the process chamber.

In another embodiment, a diffuser plate comprises a body having a topsurface and a bottom surface, a plurality of gas passages between thetop surface the bottom surface, and an outer region and an inner regionwherein the body between the top and the bottom of the outer region isthicker than the body between the top and the bottom of the innerregion.

In another embodiment, a method of making a gas diffuser plate for aplasma processing chamber comprises making a gas diffuser plate to havean upstream side and a down stream side, and a plurality of gas passagespassing between the upstream and downstream sides of the diffuser plate,and machining the downstream surface to make the downstream surfaceconcave.

In yet another embodiment, a method of making a gas diffuser plate for aplasma processing chamber comprises bending a diffuser plate that havean upstream side and a down stream side to make the downstream surfaceconcave and the upstream surface convex, making a plurality of gaspassages passing between the upstream and downstream sides of thediffuser plate by making hollow cathode cavities to the same depth froma fictitious flat downstream surface, and making all gas passages tohave the same-size orifice holes which are connected to the hollowcathode cavities.

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present invention can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 depicts a cross-sectional schematic view of a bottom gate thinfilm transistor.

FIG. 2 is a schematic cross-sectional view of an illustrative processingchamber having one embodiment of a gas distribution plate assembly ofthe present invention.

FIG. 3 depicts a cross-sectional schematic view of a gas diffuser plate.

FIG. 4A shows the process flow of depositing a thin film on a substratein a process chamber with a diffuser plate.

FIG. 4B shows the deposition rate measurement across a 1500 mm by 1800mm substrate collected from deposition with a diffuser plate withuniform diffuser holes diameters and depths.

FIG. 5 shows 2 sides (501 and 502) of the substrate that are close tothe sides with pumping channels closed and the 5 measurement locationson a substrate.

FIG. 6A (Prior Art) illustrates the concept of hollow cathode effect.

FIGS. 6B-6G illustrates various designs of hollow cathode cavities.

FIG. 7A shows the definition of diameter “D”, the depth “d” and theflaring angle “ ” of the bore that extends to the downstream end of agas passage.

FIG. 7B shows the dimensions of a gas passage.

FIG. 7C shows the dimensions of a gas passage.

FIG. 7D shows the dimensions of a gas passage.

FIG. 7E shows the distribution of gas passages across a diffuser plate.

FIG. 8 shows the deposition rate measurement across a 1500 mm by 1800 mmsubstrate collected from deposition with a diffuser plate with adistribution of gas passages across the diffuser plate as shown in FIG.7E.

FIG. 9A shows the process flow of making a diffuser plate.

FIG. 9B shows a bent diffuser plate.

FIG. 9C shows a diffuser plate that was previously bent and the sidethat facing the downstream side was machined to be flat.

FIG. 9D shows the distribution of depths of diffuser bores that extendsto the downstream ends of gas passages of a diffuser plate used toprocess 1500 mm by 1850 mm substrates.

FIG. 9E shows the measurement of deposition rates across a 1500 mm by1850 mm substrate.

FIG. 9F shows the distribution of depths of diffuser bores that extendsto the downstream ends of gas passages of a diffuser plate used toprocess 1870 mm by 2200 mm substrates.

FIG. 9G shows the measurement of deposition rates across an 1870 mm by2200 mm substrate.

FIG. 10A shows the process flow of bending the diffuser plate by athermal process.

FIG. 10B shows the diffuser plate on the supports in the thermalenvironment that could be used to bend the diffuser plate.

FIG. 10C shows the convex diffuser plate on the supports in the thermalenvironment.

FIG. 11A shows the process flow of bending the diffuser plate by avacuum process.

FIG. 11B shows the diffuser plate on the vacuum assembly.

FIG. 11C shows the convex diffuser plate on the vacuum assembly.

FIG. 12A shows the process flow of creating a diffuser plate withvarying diameters and depths of bores that extends to the downstreamside of the diffuser plate.

FIG. 12B shows the cross section of a diffuser plate with varyingdiameters and depths of bores that extends to the downstream side of thediffuser plate.

FIG. 12C shows a diffuser plate with substantially identical diffuserholes from center to edge of the diffuser plate.

FIG. 12D shows the diffuser plate of FIG. 12C after the bottom surfacehas been machined into a concave shape.

FIG. 12E shows the diffuser plate of FIG. 12D after its bottom surfacehas been pulled substantially flat.

FIG. 12F shows a diffuser plate, without any diffuser holes, that hasbeen bent into a concave (bottom surface) shape.

FIG. 12G shows the diffuser plate of FIG. 12F with diffuser holes.

FIG. 12H shows the diffuser plate of FIG. 12G after its bottom surfacehas been pulled substantially flat.

FIG. 12I shows a diffuser plate with diffuser holes in multiple zones.

FIG. 12J shows a diffuser plate with mixed hollow cathode cavitydiameters and the inner region hollow cathode cavity volume and/orsurface area density is higher than the outer region hollow cathodecavity volume and/or surface area density.

FIG. 12K shows a diffuser plate with most of the hollow cathode cavitiesthe same, while there are a few larger hollow cathode cavities near theedge of the diffuser plate.

FIG. 13 shows the downstream side view of a diffuser plate with varyingdiffuser hole densities.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION

The invention generally provides a gas distribution assembly forproviding gas delivery within a processing chamber. The invention isillustratively described below in reference to a plasma enhancedchemical vapor deposition system configured to process large areasubstrates, such as a plasma enhanced chemical vapor deposition (PECVD)system, available from AKT, a division of Applied Materials, Inc., SantaClara, Calif. However, it should be understood that the invention hasutility in other system configurations such as etch systems, otherchemical vapor deposition systems and any other system in whichdistributing gas within a process chamber is desired, including thosesystems configured to process round substrates.

FIG. 1 illustrates cross-sectional schematic views of a thin filmtransistor structure. A common TFT structure is the back channel etch(BCE) inverted staggered (or bottom gate) TFT structure shown in FIG. 1.The BCE process is preferred, because the gate dielectric (SiN), and theintrinsic as well as n+ doped amorphous silicon films can be depositedin the same PECVD pump-down run. The BCE process shown here involvesonly 5 patterning masks. The substrate 101 may comprise a material thatis essentially optically transparent in the visible spectrum, such as,for example, glass or clear plastic. The substrate may be of varyingshapes or dimensions. Typically, for TFT applications, the substrate isa glass substrate with a surface area greater than about 500 mm². A gateelectrode layer 102 is formed on the substrate 101. The gate electrodelayer 102 comprises an electrically conductive layer that controls themovement of charge carriers within the TFT. The gate electrode layer 102may comprise a metal such as, for example, aluminum (Al), tungsten (W),chromium (Cr), tantalum (Ta), or combinations thereof, among others. Thegate electrode layer 102 may be formed using conventional deposition,lithography and etching techniques. Between the substrate 101 and thegate electrode layer 102, there may be an optional insulating material,for example, such as silicon dioxide (SiO₂) or silicon nitride (SiN),which may also be formed using an embodiment of a PECVD system describedin this invention. The gate electrode layer 102 is then lithographicallypatterned and etched using conventional techniques to define the gateelectrode.

A gate dielectric layer 103 is formed on the gate electrode layer 102.The gate dielectric layer 103 may be silicon dioxide (SiO₂), siliconoxynitride (SiON), or silicon nitride (SiN), deposited using anembodiment of a PECVD system described in this invention. The gatedielectric layer 103 may be formed to a thickness in the range of about100 Å to about 6000 Å.

A bulk semiconductor layer 104 is formed on the gate dielectric layer103. The bulk semiconductor layer 104 may comprise polycrystallinesilicon (polysilicon) or amorphous silicon (—Si), which could bedeposited using an embodiment of a PECVD system described in thisinvention or other conventional methods known to the art. Bulksemiconductor layer 104 may be deposited to a thickness in the range ofabout 100 Å to about 3000 Å. A doped semiconductor layer 105 is formedon top of the semiconductor layer 104. The doped semiconductor layer 105may comprise n-type (n+) or p-type (p+) doped polycrystalline(polysilicon) or amorphous silicon (—Si), which could be deposited usingan embodiment of a PECVD system described in this invention or otherconventional methods known to the art. Doped semiconductor layer 105 maybe deposited to a thickness within a range of about 100 Å to about 3000Å. An example of the doped semiconductor layer 105 is n+ doped —Si film.The bulk semiconductor layer 104 and the doped semiconductor layer 105are lithographically patterned and etched using conventional techniquesto define a mesa of these two films over the gate dielectric insulator,which also serves as storage capacitor dielectric. The dopedsemiconductor layer 105 directly contacts portions of the bulksemiconductor layer 104, forming a semiconductor junction.

A conductive layer 106 is then deposited on the exposed surface. Theconductive layer 106 may comprise a metal such as, for example, aluminum(Al), tungsten (W), molybdenum (Mo), chromium (Cr), tantalum (Ta), andcombinations thereof, among others. The conductive layer 106 may beformed using conventional deposition techniques. Both the conductivelayer 106 and the doped semiconductor layer 105 may be lithographicallypatterned to define source and drain contacts of the TFT. Afterwards, apassivation layer 107 may be deposited. Passivation layer 107conformably coats exposed surfaces. The passivation layer 107 isgenerally an insulator and may comprise, for example, silicon dioxide(SiO₂) or silicon nitride (SiN). The passivation layer 107 may be formedusing, for example, PECVD or other conventional methods known to theart. The passivation layer 107 may be deposited to a thickness in therange of about 1000 Å to about 5000 Å. The passivation layer 107 is thenlithographically patterned and etched using conventional techniques toopen contact holes in the passivation layer.

A transparent conductor layer 108 is then deposited and patterned tomake contacts with the conductive layer 106. The transparent conductorlayer 108 comprises a material that is essentially optically transparentin the visible spectrum and is electrically conductive. Transparentconductor layer 108 may comprise, for example, indium tin oxide (ITO) orzinc oxide, among others. Patterning of the transparent conductive layer108 is accomplished by conventional lithographical and etchingtechniques.

The doped or un-doped (intrinsic) amorphous silicon (—Si), silicondioxide (SiO2), silicon oxynitride (SiON) and silicon nitride (SiN)films used in liquid crystal displays (or flat panels) could all bedeposited using an embodiment of a plasma enhanced chemical vapordeposition (PECVD) system described in this invention. The TFT structuredescribed here is merely used as an example. The current inventionapplies to manufacturing any devices that are applicable.

FIG. 2 is a schematic cross-sectional view of one embodiment of a plasmaenhanced chemical vapor deposition system 200, available from AKT, adivision of Applied Materials, Inc., Santa Clara, Calif. The system 200generally includes a processing chamber 202 coupled to a gas source 204.The processing chamber 202 has walls 206 and a bottom 208 that partiallydefine a process volume 212. The process volume 212 is typicallyaccessed through a port (not shown) in the walls 206 that facilitatemovement of a substrate 240 into and out of the processing chamber 202.The walls 206 and bottom 208 are typically fabricated from a unitaryblock of aluminum or other material compatible with processing. Thewalls 206 support a lid assembly 210 that contains a pumping plenum 214that couples the process volume 212 to an exhaust port (that includesvarious pumping components, not shown).

A temperature controlled substrate support assembly 238 is centrallydisposed within the processing chamber 202. The support assembly 238supports a glass substrate 240 during processing. In one embodiment, thesubstrate support assembly 238 comprises an aluminum body 224 thatencapsulates at least one embedded heater 232. The heater 232, such as aresistive element, disposed in the support assembly 238, is coupled toan optional power source 274 and controllably heats the support assembly238 and the glass substrate 240 positioned thereon to a predeterminedtemperature. Typically, in a CVD process, the heater 232 maintains theglass substrate 240 at a uniform temperature between about 150 to atleast about 460 degrees Celsius, depending on the deposition processingparameters for the material being deposited.

Generally, the support assembly 238 has a lower side 226 and an upperside 234. The upper side 234 supports the glass substrate 240. The lowerside 226 has a stem 242 coupled thereto. The stem 242 couples thesupport assembly 238 to a lift system (not shown) that moves the supportassembly 238 between an elevated processing position (as shown) and alowered position that facilitates substrate transfer to and from theprocessing chamber 202. The stem 242 additionally provides a conduit forelectrical and thermocouple leads between the support assembly 238 andother components of the system 200.

A bellows 246 is coupled between support assembly 238 (or the stem 242)and the bottom 208 of the processing chamber 202. The bellows 246provides a vacuum seal between the chamber volume 212 and the atmosphereoutside the processing chamber 202 while facilitating vertical movementof the support assembly 238.

The support assembly 238 generally is grounded such that RF powersupplied by a power source 222 to a gas distribution plate assembly 218positioned between the lid assembly 210 and substrate support assembly238 (or other electrode positioned within or near the lid assembly ofthe chamber) may excite gases present in the process volume 212 betweenthe support assembly 238 and the distribution plate assembly 218. The RFpower from the power source 222 is generally selected commensurate withthe size of the substrate to drive the chemical vapor depositionprocess.

The support assembly 238 additionally supports a circumscribing shadowframe 248. Generally, the shadow frame 248 prevents deposition at theedge of the glass substrate 240 and support assembly 238 so that thesubstrate does not stick to the support assembly 238. The supportassembly 238 has a plurality of holes 228 disposed therethrough thataccept a plurality of lift pins 250. The lift pins 250 are typicallycomprised of ceramic or anodized aluminum. The lift pins 250 may beactuated relative to the support assembly 238 by an optional lift plate254 to project from the support surface 230, thereby placing thesubstrate in a spaced-apart relation to the support assembly 238.

The lid assembly 210 provides an upper boundary to the process volume212. The lid assembly 210 typically can be removed or opened to servicethe processing chamber 202. In one embodiment, the lid assembly 210 isfabricated from aluminum (Al). The lid assembly 210 includes a pumpingplenum 214 formed therein coupled to an external pumping system (notshown). The pumping plenum 214 is utilized to channel gases andprocessing by-products uniformly from the process volume 212 and out ofthe processing chamber 202.

The lid assembly 210 typically includes an entry port 280 through whichprocess gases provided by the gas source 204 are introduced into theprocessing chamber 202. The entry port 280 is also coupled to a cleaningsource 282. The cleaning source 282 typically provides a cleaning agent,such as dissociated fluorine, that is introduced into the processingchamber 202 to remove deposition by-products and films from processingchamber hardware, including the gas distribution plate assembly 218.

The gas distribution plate assembly 218 is coupled to an interior side220 of the lid assembly 210. The gas distribution plate assembly 218 istypically configured to substantially follow the profile of the glasssubstrate 240, for example, polygonal for large area flat panelsubstrates and circular for wafers. The gas distribution plate assembly218 includes a perforated area 216 through which process and other gasessupplied from the gas source 204 are delivered to the process volume212. The perforated area 216 of the gas distribution plate assembly 218is configured to provide uniform distribution of gases passing throughthe gas distribution plate assembly 218 into the processing chamber 202.Gas distribution plates that may be adapted to benefit from theinvention are described in commonly assigned U.S. patent applicationSer. No. 09/922,219, filed Aug. 8, 2001 by Keller et al., U.S. patentapplication Ser. No. 10/140,324, filed May 6, 2002 by Yim et al., andSer. No. 10/337,483, filed Jan. 7, 2003 by Blonigan et al., U.S. Pat.No. 6,477,980, issued Nov. 12, 2002 to White et al., U.S. patentapplication Ser. No. 10/417,592, filed Apr. 16, 2003 by Choi et al., andU.S. patent application Ser. No. 10/823,347, filed on Apr. 12, 2004 byChoi et al., which are hereby incorporated by reference in theirentireties.

The gas distribution plate assembly 218 typically includes a diffuserplate (or distribution plate) 258 suspended from a hanger plate 260. Thediffuser plate 258 and hanger plate 260 may alternatively comprise asingle unitary member. A plurality of gas passages 262 are formedthrough the diffuser plate 258 to allow a predetermined distribution ofgas passing through the gas distribution plate assembly 218 and into theprocess volume 212. The hanger plate 260 maintains the diffuser plate258 and the interior surface 220 of the lid assembly 210 in aspaced-apart relation, thus defining a plenum 264 therebetween. Theplenum 264 allows gases flowing through the lid assembly 210 touniformly distribute across the width of the diffuser plate 258 so thatgas is provided uniformly above the center perforated area 216 and flowswith a uniform distribution through the gas passages 262.

The diffuser plate 258 is typically fabricated from stainless steel,aluminum (Al), anodized aluminum, nickel (Ni) or other RF conductivematerial. The diffuser plate 258 could be cast, brazed, forged, hotiso-statically pressed or sintered. The diffuser plate 258 is configuredwith a thickness that maintains sufficient flatness across the aperture266 as not to adversely affect substrate processing. The thickness ofthe diffuser plate 258 is between about 0.8 inch to about 2.0 inches.The diffuser plate 258 could be circular for semiconductor wafermanufacturing or polygonal, such as rectangular, for flat panel displaymanufacturing.

FIG. 3 is a partial sectional view of an exemplary diffuser plate 258that is described in commonly assigned U.S. patent application Ser. No.10/417,592, titled “Gas Distribution Plate Assembly for Large AreaPlasma Enhanced Chemical Vapor Deposition”, filed on Apr. 16, 2003. Thediffuser plate 258 includes a first or upstream side 302 facing the lidassembly 210 and an opposing second or downstream side 304 that facesthe support assembly 238. Each gas passage 262 is defined by a firstbore 310 coupled by an orifice hole 314 to a second bore 312 thatcombine to form a fluid path through the gas distribution plate 258. Thefirst bore 310 extends a first depth 330 from the upstream side 302 ofthe gas distribution plate 258 to a bottom 318. The bottom 318 of thefirst bore 310 may be tapered, beveled, chamfered or rounded to minimizethe flow restriction as gases flow from the first bore into the orificehole 314. The first bore 310 generally has a diameter of about 0.093 toabout 0.218 inches, and in one embodiment is about 0.156 inches.

The second bore 312 is formed in the diffuser plate 258 and extends fromthe downstream side (or end) 304 to a depth 332 of about 0.10 inch toabout 2.0 inches. Preferably, the depth 332 is between about 0.1 inch toabout 1.0 inch. The diameter 336 of the second bore 312 is generallyabout 0.1 inch to about 1.0 inch and may be flared at an angle 316 ofabout 10 degrees to about 50 degrees. Preferably, the diameter 336 isbetween about 0.1 inch to about 0.5 inch and the flaring angle 316 isbetween 20 degrees to about 40 degrees. The surface of the second bore312 is between about 0.05 inch² to about 10 inch² and preferably betweenabout 0.05 inch² to about 5 inch². The diameter of second bore 312refers to the diameter intersecting the downstream surface 304. Anexample of diffuser plate, used to process 1500 mm by 1850 mmsubstrates, has second bores 312 at a diameter of 0.250 inch and at aflare angle 316 of about 22 degrees. The distances 380 between rims 382of adjacent second bores 312 are between about 0 inch to about 0.6 inch,preferably between about 0 inch to about 0.4 inch. The diameter of thefirst bore 310 is usually, but not limited to, being at least equal toor smaller than the diameter of the second bore 312. A bottom 320 of thesecond bore 312 may be tapered, beveled, chamfered or rounded tominimize the pressure loss of gases flowing out from the orifice hole314 and into the second bore 312. Moreover, as the proximity of theorifice hole 314 to the downstream side 304 serves to minimize theexposed surface area of the second bore 312 and the downstream side 304that face the substrate, the downstream area of the diffuser plate 258exposed to fluorine provided during chamber cleaning is reduced, therebyreducing the occurrence of fluorine contamination of deposited films.

The orifice hole 314 generally couples the bottom 318 of the first hole310 and the bottom 320 of the second bore 312. The orifice hole 314generally has a diameter of about 0.01 inch to about 0.3 inch,preferably about 0.01 inch to about 0.1 inch, and typically has a length334 of about 0.02 inch to about 1.0 inch, preferably about 0.02 inch toabout 0.5 inch. The length 334 and diameter (or other geometricattribute) of the orifice hole 314 is the primary source of backpressure in the plenum 264 which promotes even distribution of gasacross the upstream side 302 of the gas distribution plate 258. Theorifice hole 314 is typically configured uniformly among the pluralityof gas passages 262; however, the restriction through the orifice hole314 may be configured differently among the gas passages 262 to promotemore gas flow through one area of the gas distribution plate 258relative to another area. For example, the orifice hole 314 may have alarger diameter and/or a shorter length 334 in those gas passages 262,of the gas distribution plate 258, closer to the wall 206 of theprocessing chamber 202 so that more gas flows through the edges of theperforated area 216 to increase the deposition rate at the perimeter ofthe glass substrate. The thickness of the diffuser plate is betweenabout 0.8 inch to about 3.0 inches, preferably between about 0.8 inch toabout 2.0 inch.

As the size of substrate continues to grow in the TFT-LCD industry,especially, when the substrate size is at least about 1000 mm by about1200 mm (or about 1,200,000 mm²), film thickness and property uniformityfor large area plasma-enhanced chemical vapor deposition (PECVD) becomesmore problematic. Examples of noticeable uniformity problems includehigher deposition rates and more compressive films in the central areaof large substrates for some high deposition rate silicon nitride films.The thickness uniformity across the substrate appears “dome shaped” withfilm in center region thicker than the edge region. The less compressivefilm in the edge region has higher Si—H content. The manufacturingrequirements for TFT-LCD include low Si—H content, for example <15atomic %, high deposition rate, for example >1500 Å/min, and lowthickness non-uniformity, for example <15%, across the substrate. TheSi—H content is calculated from FTIR (Fourier Transform Infra-Red)measurement. The larger substrates have worse “dome shape” uniformityissue. The problem could not be eliminated by process recipemodification to meet all requirements. Therefore, the issue needs to beaddressed by modifying the gas and/or plasma distribution.

The process of depositing a thin film in a process chamber is shown inFIG. 4A. The process starts at step 401 by placing a substrate in aprocess chamber with a diffuser plate. Next at step 402, flow processgas(es) through a diffuser plate toward a substrate supported on asubstrate support. Then at step 403, create a plasma between thediffuser plate and the substrate support. At step 404, deposit a thinfilm on the substrate in the process chamber. FIG. 4B shows a thicknessprofile of a silicon nitride film across a glass substrate. The size ofthe substrate is 1500 mm by 1800 mm. The diffuser plate has diffuserholes with design shown in FIG. 3. The diameter of the first bore 310 is0.156 inch. The length 330 of the first bore 310 is 1.049 inch. Thediameter 336 of the second bore 312 is 0.250 inch. The flaring angle 316of the second bore 312 is 22 degree. The length 332 of the second bore312 is 0.243 inch. The diameter of the orifice hole 314 is 0.016 inchand the length 334 of the orifice hole 314 is 0.046 inch. The SiN filmis deposited using 2800 sccm SiH₄, 9600 sccm NH₃ and 28000 sccm N₂,under 1.5 Torr, and 15000 watts source power. The spacing between thediffuser plate and the support assembly is 1.05 inch. The processtemperature is maintained at about 355° C. The deposition rate isaveraged to be 2444 Å/min and the thickness uniformity (with 15 mm edgeexclusion) is 25.1%, which is higher than the manufacturingspecification (<15%). The thickness profile shows a center thickprofile, or “dome shape” profile. Table 1 shows the film propertiesmeasured from wafers placed on the glass substrate for the above film.

TABLE 1 Measurement of thickness and film properties on a substratedeposited with SiN film. Stress Measurement Thickness (E9 Si—H WERlocation (Å) RI Dynes/cm²) (atomic %) (Å/min) Edge I 5562 1.92 −0.7 12.5664 Center 8544 1.90 −6.7 4.2 456 Edge II 6434 1.91 −1.2 10.8 665

Edge I and Edge II represent two extreme ends of the substrate withwidth at 1800 mm. The refractive index (RI), film stress, Si—Hconcentration data and wet etch rate (WER) data show a more compressivefilm near the center region in comparison to the edge region. The Si—Hconcentrations at the substrate edges are approaching the manufacturinglimit of 15%. Wet etch rate is measured by immersing the samples in aBOE (buffered oxide etch) 6:1 solution.

One theory for the cause of the center to edge non-uniformity problem isexcess residual gas between diffuser plate and substrate and in thecenter region of the substrate that could not be pumped awayeffectively, which may have caused high deposition rate and morecompressive film in the center region of the substrate. A simple testhas been designed to see if this theory would stand. As shown in FIG. 5,a thermo-resistant tape is used to block of the pumping channels 214(shown in FIG. 2) near side 501 and side 502 of substrate in a PECVDprocess chamber. The pumping channels 214 near the other two sides areleft open. Due to this, an asymmetric gas pumping situation was created.If the cause of the “dome shape” problem is due to excess residual gasthat could not be pumped away at the edge of the substrate, the use ofthermo-resistant tape near two edges of the substrate should worsen theuniformity issue and cause worse uniformity across the substrate.However, little changes has been observed comparing the depositionresults between deposition done with 2 pumping channels blocked anddeposition with all pumping channel opened (see Table 2). The diffuserplate used here has the same design and dimensions as the one used forFIG. 4B and Table 1. The SiN films in Table 2 are deposited using 3300sccm SiH₄, 28000 sccm NH₃ and 18000 sccm N₂, under 1.3 Torr, and 11000watts source power. The spacing between the diffuser plate and thesupport assembly is 0.6 inch. The process temperature is maintained atabout 355° C. Film thickness and properties are measured on location 1,2, 3, 4 and 5 (as shown in FIG. 5) on the substrates. The SiH contentshown is Table 2 is measured in atomic %.

TABLE 2 SiN thickness and film properties comparison between depositionwith all pumping channels open and with 2 pumping channels closed. Allpumping channels open 2 pumping channels blocked Stress Stress Thick-(E9 Thick- (E9 Posi- ness dynes/ SiH ness dynes/ SiH tion (Å) RI cm²)(%) (Å) RI cm²) (%) 1 6156 1.92 −4.6 11.1 5922 1.93 −3.9 11.5 2 71081.91 −5.1 8.8 7069 1.92 −5.1 9.1 3 7107 1.91 −5.1 8.5 7107 1.91 −4.8 8.94 7052 1.91 −5.0 8.1 7048 1.91 −4.6 8.5 5 6173 1.92 −4.2 10.8 6003 1.92−3.8 11.2

The results in Table 2 show little difference between the depositiondone with 2 pumping channels blocked and deposition with all pumpingchannel opened. In addition, there is little difference betweenmeasurement collected at locations 1 and 5, which should be different ifresidual gas is the cause of the problem. Therefore, the theory ofexcess residual gas between diffuser and substrate and in the centerregion of the substrate not being pumped away effectively is ruled out.

Another possible cause for the center to edge non-uniformity is plasmanon-uniformity. Deposition of films by PECVD depends substantially onthe source of the active plasma. Dense chemically reactive plasma can begenerated due to hollow cathode effect. The driving force in the RFgeneration of a hollow cathode discharge is the frequency modulated d.c.voltage Vs (the self-bias voltage) across the space charge sheath at theRF electrode. A RF hollow cathode and oscillation movement of electronsbetween repelling electric fields, Es, of the opposite sheaths are shownschematically in FIG. 6A. An electron emitted from the cathode wall,which could be the walls of the reactive gas passages that are close tothe process volume 212, is accelerated by the electric field Es acrossthe wall sheath “ ”. The electron oscillates across the inner spacebetween walls of the electrode owing to the repelling fields of theopposite wall sheaths. The electron loses energy by collisions with thegas and creates more ions. The created ions can be accelerated to thecathode walls thereby enhancing emissions of secondary electrons, whichcould create additional ions. Overall, the cavities between the cathodewalls enhance the electron emission and ionization of the gas.Flared-cone shaped cathode walls, with gas inlet diameter smaller thanthe gas outlet diameter, are more efficient in ionizing the gas thancylindrical walls. The potential Ez is created due to difference inionization efficiency between the gas inlet and gas outlet.

By changing the design of the walls of the hollow cathode cavities,which faces the substrate and are at the downstream ends of the gasdiffuser holes (or passages), that are close to the process volume 212and the arrangement (or density) of the hollow cathode cavities, the gasionization could be modified to control the film thickness and propertyuniformity. An example of the walls of the hollow cathode cavities thatare close to the process volume 212 is the second bore 312 of FIG. 3.The hollow cathode effect mainly occurs in the flared cone 312 thatfaces the process volume 212. The FIG. 3 design is merely used as anexample. The invention can be applied to other types of hollow cathodecavity designs. Other examples of hollow cathode cavity design include,but not limited to, the designs shown in FIGS. 6B-6G. By varying thevolume and/or the surface area of the hollow cathode cavity, the plasmaionization rate can be varied.

Using the design in FIG. 3 as an example, the volume of second bore (orhollow cathode cavity) 312 can be changed by varying the diameter “D”(or diameter 336 in FIG. 3), the depth “d” (or length 332 in FIG. 3) andthe flaring angle “ ” (or flaring angle 316 of FIG. 3), as shown in FIG.7A. Changing the diameter, depth and/or the flaring angle would alsochange the surface area of the bore 312. Since the center of substratehas higher deposition rate and is more compressive, higher plasmadensity is likely the cause. By reducing the bore depth, the diameter,the flaring angle, or a combination of these three parameters from edgeto center of the diffuser plate, the plasma density could be reduced inthe center region of the substrate to improve the film thickness andfilm property uniformities. Reducing the cone (or bore) depth, conediameter, flaring angle also reduces the surface area of the bore 312.FIGS. 7B, 7C and 7D show 3 diffuser passage (or diffuser hole) designsthat are arranged on a diffuser plate shown in FIG. 7E. FIGS. 7B, 7C and7D designs have the same cone (or bore) diameter, but the cone (or bore)depth and total cone (bore) surface areas are largest for FIG. 7B designand smallest for FIG. 7D design. The cone flaring angles have beenchanged to match the final cone diameter. The cone depth for FIG. 7B is0.7 inch. The cone depth for FIG. 7C is 0.5 inch and the cone depth forFIG. 7D is 0.325 inch. The smallest rectangle 710 in FIG. 7E is 500 mmby 600 mm and the diffuser holes have cone depth 0.325 inch, conediameter 0.302 inch and flare angel 45° (See FIG. 7D). The mediumrectangle in FIG. 7E is 1000 mm by 1200 mm. The diffuser holes in thearea 720 between the medium rectangle and the smallest rectangle havecone depth 0.5 inch, cone diameter 0.302 inch and flare angle 30° (SeeFIG. 7C). The largest rectangle in Figure is 1500 mm by 1800 mm. Thediffuser holes in the area 730 between the largest rectangle and themedium rectangle have cone depth 0.7 inch, cone diameter 0.302 inch andflare angle 22° (See FIG. 7B) The orifice holes diameters are all 0.03inch and holes depths are all 0.2 inch for FIGS. 7B, 7C and 7D. Thethickness of the three diffuser plates are all 1.44 inch. The diametersfor first bore 310 of FIGS. 7B, 7C and 7D are all 0.156 inch and thedepth are 0.54 inch (FIG. 7B), 0.74 inch (FIG. 7C) and 0.915 inch (FIG.7C) respectively.

FIG. 8 shows the deposition rate across the substrate. Region Icorrelates to the area under “0.325 inch depth” cones, while regions IIand III correlates to “0.5 inch depth” (region II) and “0.7 inch depth”(region III) respectively. Table 3 shows the measurement of filmthickness and properties across the substrate. The SiN film in Table 3is deposited using 3300 sccm SiH₄, 28000 sccm NH₃ and 18000 sccm N₂,under 1.3 Torr, and 11000 watts source power. The spacing between thediffuser plate and the support assembly is 0.6 inch. The processtemperature is maintained at about 355° C. The locations 1, 2, 3, 4 and5 are the same locations indicated in FIG. 5.

TABLE 3 SiN film thickness and property measurement with diffuser platewith 3 regions of varying cone depths. Stress Cone depth Thickness (E9SiH Position (inch) (Å) RI dynes/cm²) (atomic %) 1 0.7 6060 1.924 −4.099.10 2 0.5 6631 1.921 −5.49 9.66 3 0.325 5659 1.915 −2.02 12.34 4 0.56956 1.916 −5.45 9.37 5 0.7 6634 1.917 −4.14 8.83

The results show that reducing the cone depth and cone surface areareduces the deposition rate. The results also show that reducing thevolume and/or surface area of hollow cathode cavity reduces thedeposition rate. The reduction of the plasma deposition rate reflects areduction in plasma ionization rate. Since the change of cone depth andtotal cone surface area from region I to region II to region III is notsmooth, the deposition rates across the substrate shows three regions.Regions I, II and III on the substrate match the diffuser holes regions710, 720 and 730. This indicates that changing the hollow cathode cavitydesign can change the plasma ionization rate and also the importance ofmaking the changes smooth and gradual.

There are many ways to gradually change hollow cathode cavities frominner regions of the diffuser plate to the outer regions of the diffuserplate to improve plasma uniformity. One way is to first bend thediffuser plate, which has identical gas diffusing passages across thediffuser plate, to a pre-determined curvature and afterwards machine outthe curvature to leave the surface flat. FIG. 9A shows the process flowof this concept. The process starts by bending the diffuser plate tomake it convex at step 901, followed by machining out the curvature ofthe convex diffuser plate to make the diffuser plate surface flat atstep 902. FIG. 9B shows a schematic drawing of a convex diffuser platewith an exemplary diffuser hole (or gas passage) 911 at the edge (andouter region) and an exemplary diffuser hole 912 in the center (andinner region) as diffuser holes. The diffuser holes 911 and 912 areidentical before the bending process and are simplified drawings ofdiffuser holes as shown in FIGS. 3 and 7A. However, the invention can beused for any diffuser holes designs. The design in FIG. 3 is merely usedfor example. Diffuser plate downstream surface 304 faces the processvolume 212. The gradual changing distance between the 913 surface andthe flat 914 surface (dotted due to its non-existence) shows thecurvature. The edge diffuser cone 915 and center diffuser cone 916 areidentical in size and shape prior to the bending process. FIG. 9C showsthe schematic drawing of a diffuser plate after the curvature has beenmachined out. The surface facing the process volume 212 is machined to914 (a flat surface), leaving center cone 918 significantly shorter thanthe edge cone 917. Since the change of the cone size (volume and/orsurface area) is created by bending the diffuser plate followed bymachining out the curvature, the change of the cone size (volume and/orsurface area) from center to edge is gradual. The center cone 918 wouldhave diameter “D” and depth “d” smaller than the edge cone 917. Thedefinition of cone diameter “D” and cone depth “d” can be found in thedescription of FIG. 7A.

FIG. 9D shows the depth “d” of the bores 312 (or cone) that extend tothe downstream side of an exemplary diffuser plate, which is used toprocess 1500 mm by 1850 mm substrates. The diffuser plate has diffuserholes with design shown in FIG. 7A. The diameter of the first bore 310is 0.156 inch. The length 330 of the first bore 310 is 1.049 inch. Thediameter 336 of the second bore 312 is 0.250 inch. The flaring angle 316of the second bore 312 is 22 degree. The length 332 of the second bore312 is 0.243 inch. The diameter of the orifice hole 314 is 0.016 inchand the length 334 of the orifice hole 314 is 0.046 inch. Themeasurement of depths of the second bores in FIG. 9D shows a gradualincreasing of bore depth 332 (or “d” in FIG. 7A) from center of thediffuser plate to the edge of the diffuser plate. Due to the bending andmachining processes, the diameter 336 (or “D” in FIG. 7A) of the bore312 also gradually increases from center of the diffuser plate to theedge of the diffuser plate.

FIG. 9E shows the thickness distribution across a substrate depositedwith SiN film under a diffuser plate with a design described in FIGS.9B, 9C and 9D. The size of substrate is 1500 mm by 1850 mm, which isonly slightly larger than the size of substrate (1500 mm by 1800 mm) inFIG. 4B and Table 1. Typically, the diffuser plate sizes scale with thesubstrate sizes. The diffuser plate used to process 1500 mm by 1850 mmsubstrates is about 1530 mm by 1860 mm, which is slightly larger thanthe diffuser plate used to process 1500 mm by 1800 mm substrates(diffuser plate about 1530 mm by 1829 mm). The thickness uniformity isimproved to 5.0%, which is much smaller than 25.1% for film in FIG. 4B.Table 4 shows the film property distribution across the substrate. Thediffuser plate has diffuser holes with design shown in FIG. 7A. Thediameter of the first bore 310 is 0.156 inch. The length 330 of thefirst bore 310 is 1.049 inch. The diameter 336 of the second bore 312 is0.250 inch. The flaring angle 316 of the second bore 312 is 22 degree.The length 332 of the second bore 312 is 0.243 inch. The diameter of theorifice hole 314 is 0.016 inch and the length 334 of the orifice hole314 is 0.046 inch. The SiN films in FIG. 9E and Table 4 are depositedusing 2800 sccm SiH₄, 9600 sccm NH₃ and 28000 sccm N₂, under 1.5 Torr,and 15000 watts source power. The spacing between the diffuser plate andthe support assembly is 1.05 inch. The process temperature is maintainedat about 355° C. Edge I and Edge II represent two extreme ends of thesubstrate, as described in Table 1 measurement. The film thickness andproperty data in Table 4 show much smaller center to edge variationcompared to the data in Table 1.

TABLE 4 SiN film thickness and property measurement using a diffuserplate with gradually varied bore depths and diameters from center toedge for a 1500 mm by 1850 mm substrate. Stress Measurement Thickness(E9 Si—H WER location (Å) RI Dynes/cm²) (atomic %) (Å/min) Edge I 64051.92 −0.7 13.3 451 Center 6437 1.91 −1.8 12.7 371 Edge II 6428 1.92 −1.211.9 427

Comparing the data in Table 4 to the data in Table 1, which arecollected from deposition with a diffuser plate with the same diametersand depths of bores 312 across the diffuser plate, the variation ofthickness, stress, Si—H content and wet etch rate (WER) are all muchless for the data in Table 4, which is collected from deposition with adiffuser plate with gradually increasing diameters and depths of bore312 from the center to the edge of the diffuser plate. The results showthat uniformity for thickness and film properties can be greatlyimproved by gradually increasing the diameters and depths of the bores,which extend to the downstream side of the diffuser plate, from centerto edge. The wet etch rates in the tables are measured by immersing thesamples in a BOE 6:1 solution.

FIG. 9F shows the depth “d” measurement of the bores 312 across anexemplary diffuser plate, which is used to process 1870 mm by 2200 mmsubstrates Curve 960 shows an example of an ideal bore depthdistribution the diffuser plate. The measurement of depths of the boresin FIG. 9F shows a gradual increasing of bore depth from center of thediffuser plate to the edge of the diffuser plate. The downstream borediameter would also gradually increase from center of the diffuser plateto the edge of the diffuser plate.

FIG. 9G shows the thickness distribution across a substrate depositedwith SiN film under a diffuser plate with a design similar to the onedescribed in FIGS. 9B, 9C and 9F. The size of the substrate is 1870 mmby 2200 mm. Table 5 shows the film property distribution across thesubstrate. The diffuser plate has diffuser holes with design shown inFIG. 7A. The diameter of the first bore 310 is 0.156 inch. The length330 of the first bore 310 is 0.915 inch. The diameter 336 of the secondbore 312 is 0.302 inch. The flaring angle 316 of the second bore 312 is22 degree. The length 332 of the second bore 312 is 0.377 inch. Thediameter of the orifice hole 314 is 0.018 inch and the length 334 of theorifice hole 314 is 0.046 inch. The SiN films in Table 5 are depositedusing 5550 sccm SiH₄, 24700 sccm NH₃ and 61700 sccm N₂, under 1.5 Torr,and 19000 watts source power. The spacing between the diffuser plate andthe support assembly is 1.0 inch. The process temperature is maintainedat about 350° C. Edge I and Edge II represent two extreme ends of thesubstrate, as described in Table 1 measurement. The film thickness andproperty data in Table 5 show much smaller center to edge variationcompared to the data in Table 1. The thickness uniformity is 9.9%, whichis much better than 25.1% for film in FIG. 4B. The data shown in FIG. 4Band Table 1 are film thickness and property data on smaller substrate(1500 mm by 1800 mm), compared to the substrate (1870 mm by 2200 mm) fordata in FIG. 9G and Table 5. Thickness and property uniformities areexpected to be worse for larger substrate. The uniformity of 9.9% andthe improved film property data in Table 5 by the new design show thatthe new design, with gradual increasing diameters and depths of diffuserbores extended to the downstream side of the diffuser plate, greatlyimproves the plasma uniformity and process uniformity.

TABLE 5 SiN film thickness and property measurement using a diffuserplate with gradually varied bore depths and diameters from center toedge for an 1870 mm by 2200 mm substrate. Stress Measurement Thickness(E9 Si—H WER location (Å) RI Dynes/cm²) (atomic %) (Å/min) Edge I 58141.94 −0.3 16.4 509 Center 5826 1.93 0.8 17.3 716 Edge II 5914 1.92 −0.613.9 644

Although the exemplary diffuser plate described here is rectangular, theinvention applies to diffuser plate of other shapes and sizes. One thingto note is that the convex downstream surface does not have to bemachined to be completely flat across the entire surface. As long as thediameters and depths of the bores are increased gradually from center toedge of the diffuser plate, the edge of the diffuser plate could be leftun-flattened.

There are also many ways to create curvature of the diffuser plate. Oneway is to thermally treat the diffuser plate at a temperature that thediffuser plate softens, such as a >400° C. temperature for aluminum, fora period of time by supporter only the edge of the diffuser plate. Whenthe metal diffuser plate softens under the high temperature treatment,the gravity would pull center of the diffuser plate down and thediffuser plate would become curved. FIG. 10A shows the process flow 1000of such thermal treatment. First, at step 1001 place the diffuser plate,which already has diffuser holes in it, in an environment 1005 orchamber that could be thermally controlled and place the diffuser plate1010 on a support 1020 that only support the edge of the diffuser plate(See FIG. 10B). The diffuser plate facing down is the downstream surface304 of the diffuser plate. Afterwards at step 1002, raise thetemperature of the environment and treat the diffuser plate at a thermalcondition at a temperature that the diffuser plate softens. Oneembodiment is to keep the thermal environment at a constant treatmenttemperature (iso-thermal), once the constant treatment temperature hasbeen reached. After the curvature of the diffuser plate has reached thedesired curvature, stop the thermal treatment process at step 1003. Notethat in the thermal environment, optional diffuser support 1030 could beplaced under diffuser plate 1010 at support height 1035 lower than thesupport height 1025 of support 1020 and at a support distance 1037shorter than the support distance 1027 of support 1020. The optionalsupport 1030 could help determine the diffuser curvature and could bemade of elastic materials that could withstand temperature greater than400° C. (the same temperature as the thermal conditioning temperature)and would not damage the diffuser plate surface. FIG. 10C shows that thecurved diffuser plate 1010 resting on the diffuser plate supports 1020and 1030 after the bending process.

Another way to create curvature is to use vacuum to smoothly bend thediffuser plate to a convex shape. FIG. 11A shows the process flow 1100of such bending by vacuum process. First, at step 1101 place thediffuser plate, which already has diffuser holes in it and thedownstream side 304 facing down, on a vacuum assembly 1105 and seal theupstream end 302 of the diffuser plate with a cover. The material usedto cover (or seal) the upstream end of the diffuser plate must be strongenough to keep its integrity under vacuum. The vacuum assembly onlysupports the diffuser plate at the edge (See FIG. 11B) by diffuser plateholder 1120. The vacuum assembly 1105 is configured to have a pumpchannel 1150 to pull vacuum in the volume 1115 between the diffuserplate and the vacuum assembly 1105 when the upstream end of the diffuserplate is covered. The pumping channel 1150 in FIGS. 11B and 11C aremerely used to demonstrate the concept. There could be more than onepumping channels placed at different locations in the vacuum assembly1105. Afterwards at step 1102, pull vacuum in the volume 1115 betweenthe diffuser plate and the diffuser plate holder. When the curvature ofthe diffuser plate has reached the desired curvature, stop the vacuumingprocess at step 1103 and restore the pressure of the volume 1115 betweenthe diffuser plate and the vacuum assembly to be equal to thesurrounding environment 1140 to allow the diffuser plate to be removedfrom the vacuum assembly 1105. Note that in the vacuum assembly,optional diffuser support 1130 could be placed under diffuser plate 1110at support height 1135 lower than the support height 1125 of thediffuser plate support 1120 and at a support distance 1137 shorter thanthe support distance 1127 of support 1120. The optional support couldhelp determine the diffuser curvature and could be made of materials,such as rubber, that would not damage the diffuser plate surface. FIG.11C shows that the curved diffuser plate 1110 resting on the diffuserplate supports 1120 and 1130 after the bending process.

Another way to change the downstream cone (312 in FIG. 3) depth, conediameter, cone flaring angle or a combination of these three parametersis by drilling the diffuser holes with varying cone depth, cone diameteror cone flaring angles from center of the diffuser plate to the edge ofthe diffuser plate. The drilling can be achieved by computer numericallycontrolled (CNC) machining. FIG. 12A shows the process flow of such aprocess 1200. The process 1200 starts at step 1230 by creating boresthat extend to the downstream side of a diffuser plate with graduallyincreasing bore depths and/or bore diameters from center to edge of thediffuser plate. The flaring angle can also be varied from center to edgeof the diffuser plate. Next at step 1240, the process is completed bycreating the remaining portions of the gas passages of the diffuserplate. The downstream cones can be created by using drill tools. Ifdrill tools with the same flaring angle are used across the diffuserplate, the cone flaring angles would stay constant and cone depth andcone diameter are varied. The cone diameter would be determined by theflaring angle and cone depth. The important thing is to vary the conedepth smoothly and gradually to ensure smooth deposition thickness andfilm property change across the substrate. FIG. 12B shows an example ofvarying cone depths and cone diameters. Diffuser hole 1201 is near thecenter of the diffuser plate and has the smallest cone depth 1211 andcone diameter 1221. Diffuser hole 1202 is between the center and edge ofthe diffuser plate and has the medium cone depth 1212 and cone diameter1222. Diffuser hole 1203 is near the edge of the diffuser plate and hasthe largest cone depth 1213 and cone diameter 1223. The cone flaringangle of all diffuser holes are the same for the design in FIG. 12B.However, it is possible to optimize deposition uniformity by varying thecone design across the diffuser plate by varying both the conediameters, cone depths and flaring angles. Changing the cone depth, conediameter and cone flaring angle affects the total cone surface area,which also affects the hollow cathode effect. Smaller cone surface arealowers the plasma ionization efficiency.

Yet another way to change the downstream bore (312 in FIG. 3) depth(“d”), and bore diameter (“D”) is by drilling identical diffuser holesacross the diffuser plate (see FIG. 12C). In FIG. 12C, the gas diffuserhole 1251 at the edge (at outer region) of the diffuser plate isidentical to the gas diffuser hole 1252 at the center (at inner region)of the diffuser plate. The downstream bore 1255 is also identical todownstream bore 1256. The downstream surface 1254 of gas diffuser plateis initially flat. Afterwards, machine downstream side of the diffuserplate to make a concave shape with center thinner than the edge. Themachining can be achieved by computer numerically controlled machiningor other types of controlled machining to make the machining processrepeatable. After machining the downstream surface 1254 to a concaveshape (surface 1259), the downstream bore 1258 at the center (an innerregion) of the diffuser plate has smaller diameter (“D”) and smallerlength (“d”) than the downstream bore 1257 at the edge (an outer region)of the diffuser plate. The diffuser plate can be left the way it is asin FIG. 12D, or downstream surface 1259 can be pulled flat as shown inFIG. 12E, or to other curvatures (not shown), to be used in a processchamber to achieve desired film results.

Yet another way to change the downstream bore (312 in FIG. 3) depth(“d”), and bore diameter (“D”) is by bending the diffuser plate withoutany diffuser hole into concave shape (See FIG. 12F). In FIG. 12F, thedownstream surface is surface 1269. Afterwards, drill the downstreambores to the same depth using the same type of drill from a fictitiousflat surface 1264 (See FIG. 12G). Although downstream bore 1268 at thecenter of the diffuser plate is drilled to the same depth from thefictitious surface 1264 as the downstream bore 1267, the diameter andlength of the downstream bore 1268 are smaller than the diameter andlength of the downstream bore 1267. The rest of the diffuser holes,which include orifice holes 1265, upstream bores 1263, and connectingbottoms, are machined to complete the diffuser holes. All orifice holesand upstream bores should have identical diameters, although it is notnecessary. The diameters and lengths of the orifice holes should be keptthe same across the diffuser plate (as shown in FIG. 12G). The orificeholes controls the back pressure. By keeping the diameters and thelengths of the orifice holes the same across the diffuser plate, theback pressure, which affects the gas flow, can be kept the same acrossthe diffuser plate. The diffuser plate can be left the way it is as inFIG. 12G, or downstream surface 1269 can be pulled flat as shown in FIG.12H, or to other curvatures (not shown), to be used in a process chamberto achieve desired film results.

The changes of diameters and/or lengths of the hollow cathode cavitiesdo not have to be perfectly continuous from center of the diffuser plateto the edge of the diffuser plate, as long the changes are smooth andgradual. It can be accomplished by a number of uniform zones arranged ina concentric pattern as long as the change from zone to zone issufficiently small. But, there need to be an overall increase of size(volume and/or surface area) of hollow cathode cavity from the center ofthe diffuser plate to the edge of the diffuser plate. FIG. 12I shows aschematic plot of bottom view (looking down at the downstream side) of adiffuser plate. The diffuser plate is divided into N concentric zones.Concentric zones are defined as areas between an inner and an outerboundaries, which both have the same geometric shapes as the overallshape of the diffuser plate. Within each zone, the diffuser holes areidentical. From zone 1 to zone N, the hollow cathode cavity graduallyincrease in size (volume and/or surface area). The increase can beaccomplished by increase of hollow cathode cavity diameter, length,flaring angle, or a combination of these parameters.

The increase of diameters and/or lengths of the hollow cathode cavitiesfrom center to edge of the diffuser plate also do not have to apply toall diffuser holes, as long as there is an overall increase in the size(volume and/or surface area) of hollow cathode cavities per downstreamdiffuser plate surface area of the hollow cathode cavities. For example,some diffuser holes could be kept the same throughout the diffuserplate, while the rest of the diffuser holes have a gradual increase inthe sizes (volumes and/or surface areas) of the hollow cathode cavities.In another example, the diffuser holes have a gradual increase in sizes(volumes and/or surface areas) of the hollow cathode cavities, whilethere are some small hollow cathode cavities at the edge of the diffuserplate, as shown in FIG. 12J. Yet in another example, most of the hollowcathode cavities are uniform across the diffuser plate, while there area few larger hollow cathode cavities towards the edge of the diffuserplate, as shown in FIG. 12K.

We can define the hollow cathode cavity volume density as the volumes ofthe hollow cathode cavities per downstream diffuser plate surface areaof the hollow cathode cavities. Similarly, we can define the hollowcathode cavity surface area density of the hollow cathode cavity as thetotal surface areas of the hollow cathode cavities per downstreamdiffuser plate surface area of the hollow cathode cavities. The resultsabove show that plasma and process uniformities can be improved bygradual increase in either the hollow cathode cavity volume density orthe hollow cathode cavity surface area density of the hollow cathodecavities from the inner regions to the outer regions of the diffuserplate, or from center to edge of the diffuser plate.

Another way to change the film deposition thickness and propertyuniformity is by changing the diffuser holes density across the diffuserplate, while keeping the diffuser holes identical. The density ofdiffuser holes is calculated by dividing the total surface of holes ofbores 312 intersecting the downstream side 304 by the total surface ofdownstream side 304 of the diffuser plate in the measured region. Thedensity of diffuser holes can be varied from about 10% to about 100%,and preferably varied from 30% to about 100%. To reduce the “dome shape”problem, the diffuser holes density should be lowered in the innerregion, compared to the outer region, to reduce the plasma density inthe inner region. The density changes from the inner region to the outerregion should be gradual and smooth to ensure uniform and smoothdeposition and film property profiles. FIG. 13 shows the gradual changeof diffuser holes density from low in the center (region A) to high atthe edge (region B). The lower density of diffuser holes in the centerregion would reduce the plasma density in the center region and reducethe “dome shape” problem. The arrangement of the diffuser holes in FIG.13 is merely used to demonstrate the increasing diffuser holes densitiesfrom center to edge. The invention applies to any diffuser holesarrangement and patterns. The density change concept can also becombined with the diffuser hole design change to improve center to edgeuniformity. When the density of the gas passages is varied to achievethe plasma uniformity, the spacing of hollow cathode cavities at thedown stream end could exceed 0.6 inch.

The inventive concept of gradual increase of hollow cathode cavity size(volume and/or surface area) from the center of the diffuser plate tothe edge of the diffuser plate can be accomplished by a combination ofthe one of the hollow cathode cavity size (volume and/or surface area)and shape variation, with or without the diffuser hole densityvariation, with one of the diffuser plate bending method, and with oneof the hollow cathode cavity machining methods applicable. For example,the concept of increasing density of diffuser holes from the center tothe edge of the diffuser plate can be used increasing the diameter ofthe hollow cathode cavity (or downstream bore) from the center to theedge of the diffuser plate. The diffuser plate could be kept flat andthe diffuser holes are drilled by CNC method. The combination isnumerous. Therefore, the concept is very capable of meeting the filmthickness and property uniformity requirements.

Up to this point, the various embodiments of the invention are mainlydescribed to increase the diameters and lengths of the hollow cathodecavities from center of the diffuser plate to the edge of the diffuserplate to improve the plasma uniformity across the substrate. There aresituations that might require the diameter and the lengths of the hollowcathode cavities to decrease from the center of the diffuser plate tothe edge of the diffuser plate. For example, the power source might belower near the center of the substrate and the hollow cathode cavitiesneed to be larger to compensate for the lower power source. The conceptof the invention, therefore, applies to decreasing the sizes (volumesand/or areas) hollow cathode cavities from the center of the diffuserplate to the edge of the diffuser plate.

The concept of the invention applies to any design of gas diffuserholes, which includes any design of hollow cathode cavity, and anyshapes/sizes of gas diffuser plates. The concept of the inventionapplies to a diffuser plate that utilizes multiple designs of gasdiffuser holes, which include multiple designs of hollow cathodecavities. The concept of the invention applies to diffuser plate of anycurvatures and diffuser plate made of any materials, for example,aluminum (Al), tungsten (W), chromium (Cr), tantalum (Ta), orcombinations thereof, among others, and by any methods, for example,cast, brazed, forged, hot iso-statically pressed or sintered. Theconcept of the invention also applies to diffuser plate made of multiplelayers of materials that are pressed or glued together. In addition, theconcept of the invention can be used in a chamber that could be in acluster system, a stand-alone system, an in-line system, or any systemsthat are applicable.

Although several preferred embodiments which incorporate the teachingsof the present invention have been shown and described in detail, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings.

What is claimed is:
 1. A gas distribution plate assembly for a plasmaprocessing chamber, comprising: a diffuser plate element having an edge,a center, a concave upstream side and a downstream side; and inner andouter gas passages passing between the upstream and downstream sides ofthe diffuser plate element from the center to the edge of the diffuserplate element, each gas passage having: an orifice hole having a firstdiameter; and a hollow cathode cavity that is downstream of the orificehole and is at the downstream side, the hollow cathode cavity having acone or cylinder shape and a second diameter at the downstream side thatis greater than the first diameter, the second diameters or the depthsor a combination of both of the cones or cylinders increases from thecenter to the edge of the diffuser plate element, the first diametersare substantially uniform from the center to the edge of the diffuserplate element.
 2. The gas distribution plate assembly of claim 1,wherein the downstream side is concave.
 3. The gas distribution plateassembly of claim 1, wherein the diffuser plate element has a firstthickness at the edge and a second thickness at the center.
 4. The gasdistribution plate assembly of claim 3, wherein a third thicknessbetween the first thickness at the edge and the second thickness at thecenter is tapered.
 5. The gas distribution plate assembly of claim 1,wherein the orifice holes are shaped to promote an even flow of gastherethrough.
 6. The gas distribution plate assembly of claim 1, whereinthe orifice holes are configured uniformly among the gas passages. 7.The gas distribution plate assembly of claim 1, wherein the orificeholes are configured non-uniformly among the gas passages.
 8. A plasmaprocessing chamber, comprising: a diffuser plate element having an edge,a center, a concave upstream side and a downstream side; a RF powersource coupled to the diffuser plate element; inner and outer gaspassages passing between the upstream and downstream sides of thediffuser plate element from the center to the edge of the diffuser plateelement, each gas passage having: an orifice hole having a firstdiameter; and a hollow cathode cavity that is downstream of the orificehole and is at the downstream side, the hollow cathode cavity having acone or cylinder shape and a second diameter at the downstream side thatis greater than the first diameter, the second diameters or the depthsor a combination of both of the cones or cylinders increases from thecenter to the edge of the diffuser plate element, the first diametersare substantially uniform from the center to the edge of the diffuserplate element; and a substrate support adjacent the downstream side ofthe diffuser plate element.
 9. The plasma processing chamber of claim 8,wherein the downstream side is concave.
 10. The plasma processingchamber of claim 8, wherein the diffuser plate element has a firstthickness at the edge and a second thickness at the center.
 11. Theplasma processing chamber of claim 10, wherein a third thickness betweenthe first thickness at the edge and the second thickness at the centeris tapered.
 12. The plasma processing chamber of claim 8, wherein theorifice holes are shaped to promote an even flow of gas therethrough.13. The plasma processing chamber of claim 8, wherein the orifice holesare configured uniformly among the gas passages.
 14. The plasmaprocessing chamber of claim 8, wherein the orifice holes are configurednon-uniformly among the gas passages.
 15. A diffuser plate, comprising:a body having an edge, a center, a top surface and a bottom surface,wherein the top surface is concave and the bottom surface is concave; aplurality of gas passages between the top surface and the bottomsurface, from the center to the edge of the body wherein each gaspassage has: an orifice hole having a first diameter; and a hollowcathode cavity that is downstream of the orifice hole and intersects thebottom surface, the hollow cathode cavity having a cone or cylindershape and a second diameter at the downstream side that is greater thanthe first diameter, the second diameters or the depths or a combinationof both of the cones or cylinders increases from the center to the edgeof the diffuser plate, the first diameters are substantially uniformfrom the center to the edge of the diffuser plate element; and an outerregion and an inner region wherein the body between the top and thebottom of the outer region is thicker than the body between the top andthe bottom of the inner region.
 16. The diffuser plate of claim 15,wherein the body has a first thickness at the edge and a secondthickness at the center.
 17. The diffuser plate of claim 16, wherein athird thickness between the first thickness at the edge and the secondthickness at the center is tapered.
 18. The diffuser plate of claim 15,wherein the orifice holes are shaped to promote an even flow of gastherethrough.
 19. The diffuser plate of claim 15, wherein the orificeholes are configured uniformly among the gas passages.
 20. The diffuserplate of claim 15, wherein the orifice holes are configurednon-uniformly among the gas passages.